Universal folding ladder

ABSTRACT

A folding ladder is formed of several pairs of ladder sections connected by a joint. The joint includes on one section a circular locking disc concentric with the joint axis and with recesses about its periphery corresponding to the different positions of the ladder sections, and a stop member on the other section engageable in the recesses. A releasing lever is provided which lift the locking member out of the recesses. An arresting device associated with the releasing lever locks the releasing lever in its releasing position during movement of the ladder sections with respect to each other in one direction and disengages the releasing lever at the end of such movement.

United States Patent Hoffman et al.

[54] UNIVERSAL FOLDING LADDER [72] lnventors: l-lelmut Hoffman; WalterHoffman, both of Talstrasse 11, Burgstall (Murr), Ger- FOREIGN PATENTSOR APPLlCATlONS 1,531,014 5/1968 France ..l82/27 n51 3,655,012 Apr.l1,1972 Primary Examiner-Reinaldo P. Machado An0rney.lennings Bailey, Jr.

[5 7] ABSTRACT A folding ladder is formed of several pairs of laddersections connected by a joint. The joint includes on one section acircular locking disc concentric with the joint axis and with recessesabout its periphery corresponding to the different positions of theladder sections, and a stop member on the other section engageable inthe recesses. A releasing lever is provided which lift the lockingmember out of the recesses. An arresting device associated with thereleasing lever locks the releasing lever in its releasing positionduring movement of the ladder sections with respect to each other in onedirection and disengages the releasing lever at the end of suchmovement.

10 Claims, 11 Drawing Figures UNIVERSAL FOLDING LADDER The presentinvention relates to a universal-folding ladder serving for multiple useand more especially to a ladder comprising several pairs of laddersections or beams or stringes which are interconnected by joints orfittings and which can be locked in the flat or straightly extendedposition and in at least one preferred service position, each of saidjoints connecting two ladder sections and comprising a first jointmember connected to either of the said two ladder sections and having atleast one circular locking disk arranged concentrically with the jointsaxis, with recesses provided preferably at equal distances about itsperiphery which are associated to the flat or straightly extendedposition and to the different preferred service positions, respectively,and further comprising an other joint member which is rigidly connectedto the other one of the said two ladder sections and further connectedwith the locking disk of the said first joint member so as to bepivotable about a joint pin, a stop member being provided and guided onthe said second joint member which snugly fits into the differentindividual recesses, respectively, when the said ladder sections are inany of the pre-determined positions and which is released from itsengaged positionand secured in its disengaged or unlocked position by asingle releasing lever which is pivoted on the said second joint memberand is to be operated from the outside and which can be pivoted to andfro at will between an engaged or locked and a disengaged or unlockedposition and with the aid of which the stop member may be lifted off therecesses when in its engaged position.

According to the invention to the said releasing lever there isassociated an arresting or locking device engaging with and, thus,locking, the releasing lever in its operative position and disengagingfrom, and releasing, the releasing lever again when the joint membersperform a subsequent relative rotation.

The universal folding ladder with multiple use according to theinvention, which may be employed for instance as working platform,single and double ladder and the like, offers the special advantage thatthe joints can be adjusted without any difficulty and with easevirtually with one hand, and that it warrants at the same time absoluteservice reliability. With this ladder, the joint parts can be lockedjust as with ladders of the conventional type in each of the preferredpositions when the ladder is being unfolded, it being impossible tobring the joint parts into the next position unless the arresting devicehas been released first, while contrary to most of the knownarrangements no locking of the ladder parts will place between theinitial and the end position when folding the ladder together, so thatit is not necessary to operate the releasing lever at any time duringthe folding process.

These and other object, features, and advantages of the presentinvention will become further apparent from the following detaileddescription thereof, particularly when the same is read with referenceto the accompanying drawings.

FIG. 1 is a side elevation of a ladder joint or fitting according to theinvention with the outer part of the one joint member partly removed,the joint being locked in one service position and the releasing leverbeing in one first position,

FIG. 2 is a side elevation of the joint or fitting according to FIG. 1shown in the same position but with the joint unlocked and with thereleasing lever in a second position allotted thereto,

FIG. 3 is a cross-section taken along the line III-III in FIG. 1

FIG. 4 is a cross-section taken along the line IVIV in FIG.

FIG. 5 is a front elevation of a detail of another embodiment of theinvention shown in an intermediate stage during the manufacture thereof,

FIG. 6 is a cross-section similar to that shown in FIG. 3 of theembodiment according to FIG. 5,

FIG. 7 is a side elevation of the releasing lever of another embodimentof the invention with the associated spring member,

FIG. 8 is a side elevation of the joint or fitting member associatedwith the releasing lever in its disengaged or inoperative position,

FIG. 9 is a side elevation of the joint or fitting member carrying thecams with the releasing lever in its disengaged or inoperative position,

FIG. 10 is also a side elevation of the arrangement according to FIG. 9,but with the releasing lever in its engaged or operative position, and

FIG. 11 is a diagrammatic side elevation of an embodiment of the ladderrungs to be used together with the novel joint or fitting.

The novel ladder comprises several pairs of ladder sections which areinterconnected by joints or fittings 9 and which can be locked in therespective service position, each of the said fittings or jointscomprising one first joint member 11 connected to one ladder stringer orbeam or section 10 and comprising at least one circular locking disk 12of cup-shaped cross-section with preferably rectangular, for instancesquareshaped recesses distributed about its periphery in correspondencewith or according to the different individual service positions of theladder or, rather, ladder members. The number of such recesses may befor instance three (13, l4, 15) corresponding to a flat position, anobtuse-angled and an acute-angled position of the joint or fitting,i.e., to a service position of the ladder known as single ladder, doubleladder or working platform, etc., or else there may be provided only tworecesses. The locking disk 12 has a bottom surface 23 with bead-like orfin-type reinforcements forming the joint outside and a circular flange24 forming the lateral extension of such bottom surface, with the radialrecesses 13, 14, 15 being provided in the transition zone 25. In orderto enable the ladder to assume the above-mentioned different positionswhen the locking disk is provided with only two recesses, the lockingdisk of the middle joint 9 or fitting may have only recesses 13, 15spaced approximately by a central angle of l20-l40 in the directionopposite to the sense of rotation, while the locking disks of the twoouter joints may have each recesses I3, 14 spaced by approximately 6080.Furthermore, the joint or fitting 9 comprises a second joint member 17arranged essentially in parallel relation to the locking disk 12 andpivoted on the latter by means of a joint pin 16, the said second jointmember 17 being connected to the other ladder beam or section 18 andcomprising a disk 26, the said joint member 17 carrying a stop member 20which snugly fits into the recesses l3, 14 or 15 when the ladder assumesany of the individual service positions and which is loaded by a spring,for instance, a spiral spring 19 bearing with its one end against thebottom of the hole 31. The said stop member has associated to it areleasing lever 21 pivoted on the second joint member 17 and to beoperated from the outside, by means of which the stop member 20 islifted off the recesses 13, 14 or 15 when it is rotated in the directionindicated by the arrow 28.

The disk 26 which rests against the circular flange 24 of the associatedlocking disk 12 may have the form of a single or or a double disk, itswall being provided, respectively with a guide slot 27, 27a within whichthe stop member 20 is held so as to be positively connected or to have aform fit in the circumferential direction and as to be slidable in theradial direction, said stop member being held between the locking disk12 and the disk 26 of the second joint member 17, the associated spring19 arranged between the stop member 20 and the abutment 30, pressing thesaid stop member outwardly in the radial direction and into theassociated recess 13 or 13a,

. posite the stop member 33 and forming essentially anintegral part ofthe second joint part, and on the other hand indirectly against the stopmember 33 over a shoe 36 fork-shaped, for instance, which embraces twosides of the said stop member. Again, the spring 32 and the releasinglever l 21 act against diametrically opposite points of the stop member33.

Each joint or fitting may consist of only one locking disk and only onedisk of the other joint member co-operating therewith. However, thefirst joint member 11 may also comprise two parallel locking disks 12,12a interconnected in the form of a fork and connected to a ladder beamor section 10, with their circular flanges 24, 24a and recesses l3, l4and 15 arranged opposite to and in register with each other, while thesecond joint member 17 may comprise two circular disks 26, 26ainterconnected to form a drum-type box and connected to the other ladderbeam or section, the said circular disks 26, 260 being embraced by thelocking disks 12, 12a and pivoted on the latter by means of the centraljournal pin 16. In this case, the drum-shaped box encases the stopmember 20, which is guided there-within to slide in the radial directionin the guide slots 27, 27a of the circular disks 26, 26a allotted to oneanother, and encases also the pivoting releasing lever 21 which consistsof two symmetrical parts made essentially of spring steel which arerigidly interconnected on one side. The

drum-enclosed portions of the releasing lever which bear against thestop member and which are resiliently interconnected by means of thespring 59 are provided in the region of their end zone with a journalpin 56', 57' engaging a bore provided at the periphery of the associateddisk of the second joint member. The movement of any drum-enclosedportion of the releasing lever 21 or the journal pin rigidly connectedtherewith, which movement is essentially rectangular in relation to theassociated disk 26, 26a, can be controlled by means of cams or recesses60, 60'a provided in the circular flange 24, 24a of the locking disk 12,12a, and acting upon the journal pins in dependence on the relativerotary movement of the two joint members. The drum-enclosed portions ofthe releasing lever are provided in the region of their journal pinswith one recess 61' each co-operating with an associated stop memberconsisting essentially of a cam 63, 63a (FIGS. 1, 2 and 4) or a pin 64,64a (FIG. in such manner that the said stop member engages theassociated recess 61 of the releasing lever 21, thus arresting thelatter, when the releasing lever 21 is shifted in the directionindicated by the arrow 28, while the journal pins and, accordingly, theinner portions of the releasing lever are caused by the recesses 60, 60aof the locking disks to move away from the inner surfaces of theassociated disk 26, 26a and the recesses 61 of the releasing lever 21come out of engagement with the associated stop member in the case ofany subsequent relative rotation of the joint in the direction indicatedby the arrows 29 and 29a, so that the stop member 20 of the joint orfitting is released for another automatic engagement when the joint isfurther rotated in the direction indicated by the arrows 29, 29a.

In the embodiment shown in FIGS. 7 and 8, the releasing lever 80, whichis subjected to the action of the spring 81, comprises two arms 82, 83arranged at an angle of approximately 90 to one another. It is rotatablyconnected at a point 84 situated approximately midway between its endsto the associated joint member, the arm 82 of the said angular lever,which constitutes the operating end thereof, taking a positionapproximately parallel to the longitudinal center axis of the jointmember associated thereto when the angular lever is in the inoperativeposition, i.e., when the stop member is in the engaged or lockedposition. The bores 85 in the releasing lever which serve to receive thepin take the form of oblong holes arranged essentially at a right anglein relation to the longitudinal center axis of the associated jointmember, so as to allow the releasing lever slight deflections or evasivemotions in the radial direction during its rotating movement. Thewedgeshaped stop member 86 passes through opposite recesses 88 in thereleasing lever and 87 in the corresponding joint member and can bemoved on the one hand along a straight line between the engaged orlocked and the unlocked or disengaged position and, on the other hand,perform a relative movement in the direction of the lever movementbetween the stop member and the releasing lever when the latter isshifted between its two end positions. For this purpose, the recesses 87have a length equalling essentially the sum of the height of the stopmember and the path travelled by the stop member between the engaged orlocked and the unlocked or disengaged position, while the recesses 88have a width considerably greater than the width of the stop member.

The releasing lever carries at its end which faces the spring member abearing support 89 for the spiral-type spring member, which bearingsupport can be rotated on the releasing lever about an axis parallel tothe axis of rotation of the releasing lever and is provided with a holewhose bottom serves as an abutment for one end of the spring member,with the other end of the spring member acting against an intermediatemember, which comprises a shaft guided within the spiral spring andwhich carries on its upper end a cross-bar 90 seated in a depression 91provided in the wall opposite the operating end of the releasing leverand which can be pivoted about an axis approximately parallel to theaxis of rotation of the releasing lever. Accordingly, the releasinglever and the spring member co-operate in the manner of a snap actingmember, which means that the lever, once it is removed from its one endposition and shifted beyond its dead-center position, will snap into itsother end position, and vice versa.

The releasing lever can be moved only by hand into the positioncorresponding to the disengaged or unlocked position of the stop member,and against the action of the arresting or locking device. For shiftingthe lever into its disengaged or unlocked position corresponding to theengaged or locked position of the stop member, cams 95, 96, 97 areprovided which are formed by projections on that side of the lockingdisk which faces the lever, each of said cams being associated to one ofthe stop notches. The said cams co-operate with a counterface 98provided on that side of the releasing lever which faces away from thejoint member, the shape and arrangement of the said cams being such thatthey will come into effect only when the ladder members are beingunfolded, while they will remain ineffective during the folding process.When viewed from above or from the side, the cams have the shape of aquadrant with its are 101 directed to the periphery of the disk. Thecams may also be part of one cam plate. The counterface of the releasinglever, which co-operate with the earns 95, 96, 97, is provided at aboutthe center of its length with a tooth-shaped projection directed towardsthe cams and having, when viewed from the operating end towards theother end one flank 98 uniformly and slightly curved right to the toothtip and one flank 99 dropping abruptly from the tooth tip to the basisof the releasing lever, with the portion adjacent the spring memberending in a flat curve 100. When the ladder members are folded, thereleasing lever is not actuated by the cams, because when the associatedright joint member is pivoted in the clockwise direction and the otherjoint member is pivoted in the counterclockwise direction always viewedin the same direction as when regarding the drawings the curved portion98 of the releasing lever will travel along the arc-shaped portion 101of the periphery of the cam. However, when unfolding the ladder into theflat or any of the preferred positions, the releasing lever is each timeoperated by the cam corresponding to the position in question in orderto release the stop for engagement with the recess. If, thereafter, theladder members are to be further unfolded beyond the already reachedposition in which the joint members are locked, the releasing lever mustfirst be operated by hand and returned into its operative position inwhich in retains the stop member in its disengaged or unlocked position.FIGS. 9 and 10 show how the releasing member and the cams of the otherjoint part co-operate during the two movements described above.

In order to obtain the largest possible tread width without sensibleincreases of the ladder weight and the dimensions of the ladder beams orsections, one may in accordance with a further development of theinvention and with FIGS. 11 give the rungs the cross-section of apolygon, for instance a trapezoid or, preferably equalsided, trianglewith two sides inclined in relation to each other, one 111 of whichcorresponding the respective tread surface and the other 1 12corresponding to the opposite surface, the arrangement of the rungs inrelation to the beams or sections 113 being such that the convenientlycorrugated tread surface, which is comprised within one horizontal oressentially horizontal plane, forms a certain angle with thelongitudinal edges of the mating beam or section and extends preferablyover the entire width of the beam or section. In this manner, oneobtains a horizontal tread surface even when the stringers or stringerparts are inclined, and due to the typical shape any desired surface maybe used as tread surface.

Although our invention has been illustrated and described with referenceto the preferred embodiments thereof, we wish to have it understood thatit is in no way limited to the details of such embodiments, but iscapable of numerous modifications within the scope of the appendedclaims.

Having thus fully disclosed our invention, what we claim is:

l. A universal folding ladder comprising several pairs of laddersections which are interconnected by joints and which can be locked inthe straightly extended position and in at least one service position,each of said joints connecting two ladder sections and comprising afirst joint member connected to either of the said two ladder sectionsand having at least one circular locking disk arranged concentricallywith the joint axis, with recesses provided about its periphery whichare associated to the straightly extended position and to differentservice positions, respectively, and further comprising another jointmember which is rigidly connected to the other one of the said twoladder sections and further connected with the locking disk of the saidfirst joint member so as to be pivotable about a joint pin, a stopmember provided and guided on the said second joint member which snuglyfits into the different individual recesses, respectively, when the saidladder sections are in any of the pre-determined positions and which isreleased from its engaged position and secured in its disengagedposition by a single releasing lever which is pivoted on the said secondjoint member and is to be operated from the outside and which can bepivoted to and fro at will between an engaged position and a disengagedposition and with the aid of which the stop may be lifted ofi therecesses when in its engaged position, wherein to the said releasinglever there is associated an arresting device engaging with, andlocking, the releasing lever in its operative position during movementof the sections with respect to each other in one direction anddisengaging from, and releasing, the releasing lever again when thejoint members reach the end of such movement.

2. The universal folding ladder set forth in claim 1, wherein the saidarresting device retains the said releasing lever both in its operativeand in its inoperative position, wherein, further, the releasing levercan be transferred into its operative position corresponding to thedisengaged position of the stop member against the action of thearresting device only by hand and into its inoperative positioncorresponding to the engaged position of the stop member against theaction of the arresting device only by cooperating with one of the camsassociated with the different individual positions of the laddersections, and wherein, further, the shape and arrangement of the camsand their coordination with the releasing lever are such that they willbecome effective only when the ladder sections are being unfolded whileremaining ineffective when the ladder sections are being foldedtogether.

3. The universal folding ladder set forth in claim 1, wherein to thesaid releasing lever having the form of an angular lever there isassociated a spring member which is movably connected with the saidreleasing lever and which retains and locks it both in its operative andin its inoperative position, the said spring member acting in the mannerof a snap acting means so that the lever, once it has been removed fromone end position and pivoted beyond its dead-center position, will snapinto its other end position, and vice versa.

4. The universal folding ladder set forth in claim 3, wherein the otherend thereof is loaded by the spring member, wherein, further, thereleasing lever is movably supported in about the middle area betweenits ends by means of pins and oblong holes and wherein, finally, thecounterface of the said releasing lever cooperating with the cams isprovided on the lever side opposite the joint member.

-5. The universal folding ladder set forth in claim 1, wherein to thesaid recesses in the said locking disk there are associated guide slotsprovided in another disk connected coaxially to the said other jointmember which hold and guide the stop member, the said stop memberengaging the recesses in the radial direction from the periphery towardsthe center of the disk when the stop member is in its engaged position.

6. The universal folding ladder set forth in claim 1, wherein the stopmember passes through opposing recesses provided, on the one hand, inthe releasing lever between the latters support portion and the endassociated with the spring member and, on the other hand, in theassociated joint member, in such a manner that the stop member may bemovable on the one hand along a straight line between its engagedposition and its disengaged position and, may, on the other hand,perform a relative movement between the stop member and the releasinglever when the latter is pivoted, this being done by making the recessesin the associated joint member to have the form of oblong holes thelength of which corresponds approximately to the height of the stopmember plus the path travelled by the stop member between theengaged'and the disengaged position, while the recesses in the releasinglever have the shape of rectangular holes with a width considerablygreater than the width of the stop member.

7. The universal folding ladder set forth in claim 1, wherein cams,which are provided at approximately equal intervals along thecircumference consist each of a projection provided on that side of thelocking disk carrying the recesses which faces the releasing lever, thesaid projections having when viewed from above, the form of a quadrantwith the are facing the periphery of the locking disk, while one of thetwo straight boundary lines are directed radially to the center of thelocking disk and the other one of the straight boundary lines on thecorresponding point extends parallely to the tangent to thecircumference of the locking disk, the counterface of the releasinglever cooperating with the cams being, when viewed from the operatingend, curved towards the cams and interrupted at about the middle of itslength by a step facing the other side and ending towards the springmember in a fiat curve.

8. The universal folding ladder set forth in claim 1, wherein a springacting on the stop member is arranged excentrically and bears on the onehand against an abutment arranged approximately diametrically oppositethe said stop member and forming an integral part with the said secondjoint member, and on the other hand in directly against the side of thestop member facing away from the releasing lever.

9. The universal folding ladder set forth in claim 8, wherein thereleasing lever comprises two portions which can be flexibly movedtowards and away from each other, while maintaining the rotatablesupport provided by the journal pin mounted to each of the portions, thesaid two portions of the said releasing lever having one recess eachessentially in the region of the journal pin, the said recesscooperating with an associated stop member provided on the inner surfaceof the associated circular disk, such cooperation taking place in such amanner that rotating of the releasing lever and displacing of the stopmember into the or disengaged position, when the stop member of thejoint is engaged in any of the service positions, will cause the stopmember of each circular disk to engage into the associated recess in thereleasing lever and thereby arrest and lock the latter in this position,while in the case of any subsequent relative movement of the joint thejournal pins will be moved away from the inner surface of the associatedcircular disk, through the recesses provided in the locking disk, sothat the recess of the releasing lever will disenthe one end of the saidreleasing lever is the operating end and gage from the associated stopmember in a direction rectangular to the circular disk, thus releasingthe stop member of the joint for another automatic engagement or lockingmovement when the joint is rotated into another service position.

10. The universal folding ladder set forth in claim 1,

wherein the cross-section of the rungs has the shape of a polygon withtwo sides inclined in relation to each other, one of them correspondingto the opposite surface and wherein,

1. A universal folding ladder comprising several pairs of laddersections which are interconnected by joints and which can be locked inthe straightly extended position and in at least one service position,each of said joints connecting two ladder sections and comprising afirst joint member connected to either of the said two ladder sectionsand having at least one circular locking disk arranged concentricallywith the joint axis, with recesses provided about its periphery whichare associated to The straightly extended position and to differentservice positions, respectively, and further comprising another jointmember which is rigidly connected to the other one of the said twoladder sections and further connected with the locking disk of the saidfirst joint member so as to be pivotable about a joint pin, a stopmember provided and guided on the said second joint member which snuglyfits into the different individual recesses, respectively, when the saidladder sections are in any of the pre-determined positions and which isreleased from its engaged position and secured in its disengagedposition by a single releasing lever which is pivoted on the said secondjoint member and is to be operated from the outside and which can bepivoted to and fro at will between an engaged position and a disengagedposition and with the aid of which the stop may be lifted off therecesses when in its engaged position, wherein to the said releasinglever there is associated an arresting device engaging with, andlocking, the releasing lever in its operative position during movementof the sections with respect to each other in one direction anddisengaging from, and releasing, the releasing lever again when thejoint members reach the end of such movement.
 2. The universal foldingladder set forth in claim 1, wherein the said arresting device retainsthe said releasing lever both in its operative and in its inoperativeposition, wherein, further, the releasing lever can be transferred intoits operative position corresponding to the disengaged position of thestop member against the action of the arresting device only by hand andinto its inoperative position corresponding to the engaged position ofthe stop member against the action of the arresting device only bycooperating with one of the cams associated with the differentindividual positions of the ladder sections, and wherein, further, theshape and arrangement of the cams and their coordination with thereleasing lever are such that they will become effective only when theladder sections are being unfolded while remaining ineffective when theladder sections are being folded together.
 3. The universal foldingladder set forth in claim 1, wherein to the said releasing lever havingthe form of an angular lever there is associated a spring member whichis movably connected with the said releasing lever and which retains andlocks it both in its operative and in its inoperative position, the saidspring member acting in the manner of a snap acting means so that thelever, once it has been removed from one end position and pivoted beyondits dead-center position, will snap into its other end position, andvice versa.
 4. The universal folding ladder set forth in claim 3,wherein the one end of the said releasing lever is the operating end andthe other end thereof is loaded by the spring member, wherein, further,the releasing lever is movably supported in about the middle areabetween its ends by means of pins and oblong holes and wherein, finally,the counterface of the said releasing lever cooperating with the cams isprovided on the lever side opposite the joint member.
 5. The universalfolding ladder set forth in claim 1, wherein to the said recesses in thesaid locking disk there are associated guide slots provided in anotherdisk connected coaxially to the said other joint member which hold andguide the stop member, the said stop member engaging the recesses in theradial direction from the periphery towards the center of the disk whenthe stop member is in its engaged position.
 6. The universal foldingladder set forth in claim 1, wherein the stop member passes throughopposing recesses provided, on the one hand, in the releasing leverbetween the latter''s support portion and the end associated with thespring member and, on the other hand, in the associated joint member, insuch a manner that the stop member may be movable on the one hand alonga straight line between its engaged position and its disengaged Positionand, may, on the other hand, perform a relative movement between thestop member and the releasing lever when the latter is pivoted, thisbeing done by making the recesses in the associated joint member to havethe form of oblong holes the length of which corresponds approximatelyto the height of the stop member plus the path travelled by the stopmember between the engaged and the disengaged position, while therecesses in the releasing lever have the shape of rectangular holes witha width considerably greater than the width of the stop member.
 7. Theuniversal folding ladder set forth in claim 1, wherein cams, which areprovided at approximately equal intervals along the circumferenceconsist each of a projection provided on that side of the locking diskcarrying the recesses which faces the releasing lever, the saidprojections having when viewed from above, the form of a quadrant withthe arc facing the periphery of the locking disk, while one of the twostraight boundary lines are directed radially to the center of thelocking disk and the other one of the straight boundary lines on thecorresponding point extends parallely to the tangent to thecircumference of the locking disk, the counterface of the releasinglever cooperating with the cams being, when viewed from the operatingend, curved towards the cams and interrupted at about the middle of itslength by a step facing the other side and ending towards the springmember in a flat curve.
 8. The universal folding ladder set forth inclaim 1, wherein a spring acting on the stop member is arrangedexcentrically and bears on the one hand against an abutment arrangedapproximately diametrically opposite the said stop member and forming anintegral part with the said second joint member, and on the other handin directly against the side of the stop member facing away from thereleasing lever.
 9. The universal folding ladder set forth in claim 8,wherein the releasing lever comprises two portions which can be flexiblymoved towards and away from each other, while maintaining the rotatablesupport provided by the journal pin mounted to each of the portions, thesaid two portions of the said releasing lever having one recess eachessentially in the region of the journal pin, the said recesscooperating with an associated stop member provided on the inner surfaceof the associated circular disk, such cooperation taking place in such amanner that rotating of the releasing lever and displacing of the stopmember into the or disengaged position, when the stop member of thejoint is engaged in any of the service positions, will cause the stopmember of each circular disk to engage into the associated recess in thereleasing lever and thereby arrest and lock the latter in this position,while in the case of any subsequent relative movement of the joint thejournal pins will be moved away from the inner surface of the associatedcircular disk, through the recesses provided in the locking disk, sothat the recess of the releasing lever will disengage from theassociated stop member in a direction rectangular to the circular disk,thus releasing the stop member of the joint for another automaticengagement or locking movement when the joint is rotated into anotherservice position.
 10. The universal folding ladder set forth in claim 1,wherein the cross-section of the rungs has the shape of a polygon withtwo sides inclined in relation to each other, one of them correspondingto the opposite surface and wherein, further, the arrangement of therungs in relation to the ladder beams is such that the tread surface,which is comprised in an approximately horizontal plane and whichextends over substantially the whole stringer width, is inclined inrelation to the longitudinal edges of the respective stringer.